Download Unusual foramen on the posterior arch of atlas.

Suresh R Rao et al. / Journal of Science / Vol 5 / Issue 12 / 2015 / 1165-1167.
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UNUSUAL FORAMEN ON THE POSTERIOR ARCH OF ATLAS
Suresh R Rao1, Gangadhara Swamy2, Vasudha T.K2 & T.Ramesh Rao1
1
Department of Preclinical Sciences, Faculty of Medical Sciences, The University of The West Indies,
St. Augustine Trinidad & Tobago.
2
Subbiah Institute of Medical Sciences and Research Center, Shimoga, India.
ABSTRACT
Atlas vertebra with a groove for the vertebral artery , dorsal rami of first cervical nerve and venous plexus is present
on the superior surface of the posterior arch of the atlas. We found an abnormal foramina on the left posterior arch of the
atlas. The vertebral artery is vulnerable to compression in its course between foramen transversarium and the foramen
magnum during extreme rotation of the head and neck. This situation may be aggravated by the presence of posterior or
lateral bridge of the Atlas and result in compromised blood flow. The presence of the bony ring formed by posterior bridging
in the atlas vertebra has been documented in previous literatures. The knowledge of the presence of this additional foramen
will be useful for chiropractioner, orthopaedic surgeons, radiologist and neurosurgeons during a spinal adjustment and
surgical manipulation of the cervical spine.
Keywords: Atlas Vertebra, Foramina, Posterior Arch.
INTRODUCTION
Atlas, the first vertebra has a great influence on
the balance of the whole skeleton and is therefore directly
responsible for an upright posture. The atlas (C1) bone is
a ring shaped bone that supports the globe of the head on
top of the spine and, along with the axis bone beneath
(C2), allows for a greater range of movement than other
vertebrae. Cup-shaped facets on the upper surface of the
atlas bone articulate with the occipital bone of the skull
and allow nodding and facets beneath articulate with the
axis bone (C2) and allow rotation of the head. The atlas
bone has bulky masses to the sides which allow it to
support the weight of the head and has facets for the
attachment of muscles and ligaments. The central space
within the ring of the atlas bone is divided into two by a
ligament, whereby the front portion receives the process
from the axis bone beneath and the posterior portion
carries the spinal cord. Structural defects of the of atlas
vertebra are more common among the cervical vertebra
[1], comprising abnormalities includes such as partial or
total fusion of atlas vertebra with the occipital bone [2,3].
The split superior articular process, split posterior or
anterior arches, and the presence of some accessory bony
arches embracing the vertebral artery [1]. Incomplete
ossification of anterior and posterior arches, anterior arch
may be absent, posterior arch may have facets and groove
for vertebral artery may get converted into a foramen [4].
Bilateral absence of foramen transversarium [5].
CASE REPORT
During routine visual inspection of the vertebral
collection housed in the Department of Anatomy, we
noticed an abnormal foramina on the left posterior arch of
the atlas vertebra. The foramina was situated at the lateral
part of the posterior arch, behind the lateral mass of the
atlas (Figures 1 and 2). Which was almost as large as the
foramen transversarium. There were foramina tranversaria
on both transverse processes and their sizes were normal.
No such abnormality was found on the right posterior
arch of the atlas. Normal groove for the vertebral artery
was identified on both the sides. Other than this there
were no other abnormalities found.
DISCUSSION
The ossification of the posterior arch of the atlas
commence from the seventh week of intrauterine life,
proceeding perichondrally from two centres located in the
lateral masses.
Corresponding Author:- Suresh R Rao Email:- [email protected]
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Suresh R Rao et al. / Journal of Science / Vol 5 / Issue 12 / 2015 / 1165-1167.
The laminae arise from buds in these
chondrification centers and extend dorsally, being nearly
fused at birth, except for several millimetres of cartilage.
Complete fusion of the posterior arch occurs at the age of
3-5 years [6-11]. The 3/5 of the atlas ring is formed by the
posterior arch of the atlas. A wide groove immediately
behind the lateral mass for vertebral artery, dorsal rami of
first cervical nerve and venous plexus is present on the
superior surface of the posterior arch of the atlas. The
superior border of posterior arch of the atlas gives
attachment to posterior atlanto-occipital membrane. This
membrane is incomplete at each lateral border to permit
way for the vertebral artery and first cervical nerve. The
lateral edge of the membrane sometimes ossifies,
converting the groove into canal. Thus the neurovascular
groove is converted into a bony ring or a bony canal,
which is called as “retroarticular canal” or “retro-articular
vertebral artery ring” [12].
Figure 1. Probe passing through the abnormal foramen
Atlas bridges, also called ponticles, are bony
outgrowths occurring on the atlas vertebra over the third
segment of the vertebral artery, converting its groove into
a sulcus, incomplete or complete foramen [13]. These
bridges may indicate ossification of the posterior atlantooccipital membrane. The posterior bridge is found dorsal
to the lateral mass on the posterior arch of the atlas and
when complete, forms the retroarticular canal also called
a Kimmerle’s variant or arcuate foramen. [13].The
posterior bridging of the Atlas is considered as a
nonmetric trait of the infracranial skeleton [14].
Mechanism of formation of this bony ring is not clearly
understood but a number of theories have been proposed :
ossification of the connective tissue surrounding the
vertebral artery, late ossification of the lower edge of the
atlanto occipital membrane [15]. Some authors have
suggested that this trait is familial rather than age related
[16, 17].
Figure 2. Superior view of atlas vertebra
FD - facet for the dens
SAF - Superior articular facet
PA - Posterior arch of atlas
FT - Foramen transversarium
AF - Abnormal foramen
CONCLUSION
The knowledge of presence of abnormal foramen
on the posterior arch of atlas will be useful for the,
chiropracters,
orthopedic
surgeons,
radiologists,
neurosurgeons for the spinal adjustment and also during
surgical manipulation of the cervical spine. During
extreme rotation of the head and neck, the vertebral artery
is more vulnerable for compression and by the presence
of this abonormal foramen in which the vertebral artery
may passes can lead to compromised blood flow.
ACKNOWLEDGEMENT: None
CONFLICT OF INTEREST
The authors declare that they have no conflict of interest.
STATEMENT OF HUMAN AND ANIMAL RIGHTS
All procedures performed in human participants
were in accordance with the ethical standards of the
institutional research committee and with the 1964
Helsinki declaration and its later amendments or
comparable ethical standards. This article does not
contain any studies with animals performed by any of the
authors.
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